The invention relates to a method of controlling a vehicle presenting a plurality of wheels, an engine and a clinch for selectively connecting the engine to a number of the wheels, the method comprising receiving a torque control signal indicative of a demanded output torque of the engine, and observing a value of a first vehicle operation parameter being the vehicle speed or a parameter which is indicative of the vehicle speed.
A vehicle moving without a driver being in full control of it may cause considerable damages, injuries and/or casualties, in particular if the vehicle is a heavy vehicle, such as a truck or a bus. Damages may be caused not only to persons and external objects, but also to the vehicle itself, e.g. by harmful speeds for the clutch disc and gearbox bearings etc. A situation with a stray vehicle can occur in a variety of circumstances. For example, the vehicle may be standing still in a downhill slope of a road, with the engine idling, but without a parking brake activated. If in such a situation the driver is not in control of the vehicle, the vehicle can on its own start rolling due to gravity and the inclination of the road. The reason for the driver's lack of control may be e.g. that he or she has quickly fallen ill and is incapable of controlling the vehicle, or that he or she is by negligence not giving the vehicle operation his or her required attention. The driver might even have left the vehicle.
Thus, there is a desire to provide a solution that would reduce the risk of damages, injuries and casualties in situations where a vehicle moving without a driver being in full control of it.
It is desirable to decrease the risk of damage or injury in situations where a driver is not in full control of a moving vehicle.
According to an aspect of the present invention, a method is provided of controlling a vehicle presenting a plurality of wheels, an engine and a clutch for selectively connecting the engine to a number of the wheels, the method comprising
receiving a torque control signal indicative of a demanded output torque of the engine, and observing a value of a first vehicle operation parameter being the vehicle speed or a parameter which is indicative of the vehicle speed,
characterised in
controlling the clutch so as to be engaged if the received torque control signal indicates that the demanded engine torque is minimal or below a first threshold value and the observed first vehicle operation parameter value is above a second threshold value,subsequently to the step of controlling the clutch so as to be engaged, performing a test disengagement of the clutch, comprising at least partly disengaging the clutch,observing a behaviour, in response to the test disengagement, of a second vehicle operation parameter, andbased at least partly on the observation of the behaviour of the second vehicle operation parameter, determining whether to control the clutch so as to be re-engaged or disengaged.
It is understood, as is known per se, that depending on the vehicle and driveline type, the engine can be connected to some of the wheels or all of the wheels, for example to two, four, or more wheels.
It is also understood that the torque control signal can be provided by a torque control device for controlling the engine output torque. The torque control device could be of any suitable type, e.g. an accelerator pedal adapted to be manipulated by a person driving the vehicle. The step of receiving a torque control signal indicative of a demanded engine output torque may be accompanied by determining a value of a demanded engine torque.
Preferably, the clutch can be controlled so as to provide a various degrees of engagements between a full engagement and a complete disengagement. More specifically, the clutch can provide a gradually increasing level of engagement from the complete disengagement towards the full engagement, and vice versa.
Preferably, the step of controlling the clutch so as to be engaged if the received torque control signal indicates that the demanded engine torque is minimal or below a first threshold value and the observed first vehicle operation parameter value is above a second threshold value, involves engaging the clutch fully. Preferably the step of determining whether to control the clutch so as to be re-engaged or disengaged, involves determining whether to control the clutch so as to be re-engaged fully. Preferably, said step involves determining whether to control the clutch so as to be or disengaged completely.
The first vehicle operation parameter could be the vehicle speed or a parameter indicative of the vehicle speed, e.g. a parameter from which the vehicle speed can be determined. For example, the first vehicle operation parameter can be proportional to the vehicle speed, e.g. it can be the rotational speed of an input shaft or a countershaft of a transmission provided functionally between the clutch and the wheels of the vehicle. Where the first vehicle operation parameter is a parameter indicative of the vehicle speed, preferably, the first vehicle operation parameter is directly proportional to the vehicle speed. Preferably, where the first vehicle operation parameter is a parameter indicative of the vehicle speed, the first vehicle operation parameter is indicative of the vehicle speed at least when the clutch is disengaged. It is understood that where the first vehicle operation parameter is the rotational speed of an input shaft or a countershaft of a transmission, of course the vehicle speed can be determined based on said input shaft speed and the current gear ratio provided by the transmission.
In some embodiments, controlling the clutch so as to be engaged is dependent on whether the demanded engine torque is minimal. It is understood that the minimal engine torque is the lowest engine torque in an engine torque interval ranging from a minimal torque to a maximal torque. The minimal engine torque may be zero engine torque.
In some embodiments, controlling the clutch so as to be engaged can be dependent on whether the demanded engine torque is below a first threshold value. Preferably the first threshold value is predetermined. The first threshold value can be higher than zero. However, it is preferred that the first threshold value is low enough to give an indication that the torque control device is not manipulated by a driver of the vehicle.
Preferably, the second threshold value of the first vehicle operation parameter is predetermined. It may be chosen to be high enough to give a clear indication that the vehicle is moving, and low enough to provide the damage and injury risk reducing effect of the invention, as discussed below.
Thus, the clutch is controlled so as to be engaged in dependence on the received torque control signal and the observed value of the first vehicle operation parameter. Subsequently the clutch test disengagement is performed, and the behaviour, in response to the test disengagement, of the second vehicle operation parameter is observed. During the clutch test disengagement, the clutch may be semi-engaged, which may be sufficient to provide an observable change of the second vehicle operation parameter.
As discussed below, the test disengagement may be repeated, but nevertheless preferably there is no change of the clutch engagement status between the clutch engagement in dependence on the received torque control signal and the observed value of the first vehicle operation parameter, and the first subsequent clutch test disengagement.
The second vehicle operation parameter can be the vehicle speed or a parameter which is indicative of the vehicle speed. As discussed closer below, in some embodiments, the second vehicle operation parameter can be the engine speed, or a parameter which is indicative of the engine speed.
In some embodiments, the second vehicle operation parameter is identical to the first vehicle operation parameter, and in other embodiments, the second vehicle operation parameter is non-identical to the first vehicle operation parameter. Preferably, where the second vehicle operation parameter is a parameter indicative of the vehicle speed, the second vehicle operation parameter is indicative of the vehicle speed at least when the clutch is disengaged. Similarly to the first vehicle operation parameter, the second vehicle operation parameter could be a parameter from which the vehicle speed can be determined. For example, the second vehicle operation parameter can be proportional, e.g. directly proportional, to the vehicle speed.
It is understood that observing a value of the first vehicle operation parameter, and observing the behaviour of the second vehicle operation parameter, can include registering, e.g. in a controller, values of the first and second vehicle operation parameters. Further, such observations may include receiving parameter values from one or more sensors, and/or calculating the parameter values at least partly from signals received from one or more sensors.
The step of observing the behaviour of the second vehicle operation parameter, is preferably done during the test disengagement of the clutch, i.e. while the clutch is at least partly disengaged. The behaviour may include a response or a change of the second vehicle operation parameter, in response to or as a result of the test disengagement.
The determination whether to control the clutch so as to be re-engaged or disengaged, may include determining whether to control the clutch so as to be disengaged fully.
If the received torque control signal indicates that the demanded engine torque is minimal or below a first threshold value and the observed first vehicle operation parameter value is above a second threshold value, this suggests that the vehicle is moving without the accelerator pedal being depressed, which in turn suggests that the driver is not in control of the vehicle. By controlling the clutch so as to be engaged the engine will be connected to the wheels and provide engine braking of the vehicle, and thereby decrease the risk of damage or injury created by the stray vehicle.
In addition, the subsequent test sequence including the clutch test disengagement and the observation of the second vehicle operation parameter behaviour, prevents the vehicle going from the engine brake mode, to a mode where the engine is propelling the vehicle, e.g. due to the fact that the vehicle is has entered a level part or an inclined part of the road. Thus, the invention provides not only for reducing the speed of a stray vehicle in a downhill slope by engine braking, but also for reducing the vehicle speed, based on the test sequence, in a following level road part or an uphill slope, by preventing engine propulsion of the vehicle. Thereby, the risk of damage or injury caused by the stray vehicle is further decreased.
It should be mentioned that it is known per se to provide vehicle speed dependent clutch operation, e.g. for vehicle creeping or coasting modes. For example, US2011136620A1 discloses a fuel saving stop/start system, where during vehicle coasting conditions, the clutch is disengaged to reduce torque from the wheels to the shutdown engine. U.S. Pat. No. 5,928,110 and U.S. Pat. No. 5,062,049 also relate to clutch operation in certain vehicle conditions. However, the invention relates to a problem, not addressed in these known solutions, of reducing damage and injury caused by stray vehicles, and provides for using the clutch control to limit the vehicle speed as opposed to maintaining it. For example, the clutch test disengagement of the invention provides a new and inventive, yet simple and effective way of determining further clutch control to limit the vehicle speed.
Preferably, observing the behaviour of the second vehicle operation parameter comprises observing whether there is a change of the second vehicle operation parameter. Observing whether there is such a change will provide a reliable manner of determining whether the vehicle is in an engine brake mode or an engine propulsion mode. Such an observation could include observing a rate of change, i.e. a time derivative, of the second vehicle operation parameter. For example, the observation could include registering during the clutch test disengagement a first and a second value of the second vehicle operation parameter, where the second value is registered subsequently to the registration of the first value, and determining an approximate second vehicle operation parameter time derivative by dividing the difference between the first and second values with the time interval between the first and second value registrations.
Preferably, observing the behaviour of the second vehicle operation parameter comprises observing whether a change of the second vehicle operation parameter is positive or negative. This provides for determining, by monitoring the second vehicle operation parameter during said clutch test disengagement, whether the net torque from the engine is positive or not. Thereby, an engine propulsion mode may be positively and reliably identified.
Preferably, the second vehicle operation parameter is the vehicle speed or a parameter which is indicative of the vehicle speed, and the step of determining whether to control the clutch so as to be re-engaged or disengaged comprises determining to control the clutch so as to be disengaged if it is observed that the second vehicle operation parameter is decreasing. This provides for a simple strategy of disengaging the wheels from the engine if the vehicle speed drops, and otherwise re-engaging the wheels to the engine the driveline. If it is observed that the second vehicle operation parameter is increasing, or remaining un-changed, it can be determined to control the clutch so as to be re-engaged. The vehicle speed, or a parameter which is indicative of the vehicle speed, provides an indication for the clutch control decision, which is more reliable than certain other vehicle operation parameters, such as engine torque. The accuracy of the engine torque can be poor due to friction, parasitic loads, etc.
In some embodiments, the second vehicle operation parameter is the engine speed or a parameter which is indicative of the engine speed, and the step of determining whether to control the clutch so as to be re-engaged or disengaged comprises determining to control the clutch so as to be disengaged if it is observed that the second vehicle operation parameter is increasing. If it is observed that the second vehicle operation parameter is decreasing, or remaining unchanged, it can be determined to control the clutch so as to be re-engaged. The use of the engine speed, i.e. the rotational speed of the engine, or a parameter which is indicative of the engine speed, provides a beneficial alternative as a basis for the clutch control decision. E.g. where the engine speed decreases, e.g. down to idle, upon the clutch test disengagement, this is an indication that the vehicle is still in an engine brake mode, and the clutch should be reengaged. Where the engine speed increases, e.g. up to idle, upon the clutch test disengagement, this is an indication that the vehicle is propelled by the engine, and the clutch should be fully disengaged. The parameter indicative of the engine speed could be a parameter from which the engine speed can be determined. For example, the second vehicle operation parameter can be proportional, e.g. directly proportional, to the engine speed. Preferably, where the second vehicle operation parameter is a parameter indicative of the engine speed, the second vehicle operation parameter is indicative of the engine speed at least when the clutch is disengaged.
Preferably, the method comprises repeating said steps of performing a test disengagement of the clutch, observing the behaviour of the second vehicle operation parameter, and determining whether to control the clutch so as to be re-engaged or disengaged, until it is determined to control the clutch so as to be disengaged. Thereby, a repeat of the test sequence provides an effective monitoring of the vehicle while it is in the engine brake mode, and the full clutch disengagement can be executed when it is determined that the vehicle has entered the engine propulsion mode. The repeat of the test sequence can be made periodically, e.g. at predetermined time intervals. Thus, smooth periodic semi-disengagements of the clutch can be performed.
Preferably, the method comprises observing the engine speed, wherein said steps of performing a test disengagement of the clutch, observing the behaviour of the second vehicle operation parameter, and determining whether to control the clutch so as to be re-engaged or disengaged, are performed if the engine speed is below a third threshold value. Thereby, the execution of the test sequence is dependent on the engine speed being below the third threshold value. This is beneficial since it makes it un-necessary to perform the test sequence if the engine speed in itself clearly indicates that the vehicle is in an engine brake mode, e.g. if the engine speed is relatively high. The third threshold value of the engine speed is preferably predetermined. The third threshold value may be slightly higher than the engine idle speed. Thus, when the engine speed presents a reduction down to the third threshold value, this can be an indication that the vehicle is about the exit the engine brake mode, and executing the test sequence can be done to confirm this assumption.
Preferably, the test disengagement of the clutch comprises disengaging the clutch according to a ramp function. Thereby, the clutch engagement can be gradually reduced until an observable change of the second vehicle operation parameter appears, which makes it possible to execute the test sequence without disengaging the clutch more than necessary.